In an internal combustion engine with at least one variable adjusting device in its air path the cylinder filling depends on several interconnected parameters. Such a variable adjusting device in the air path of an internal combustion engine is for example a length-variable suction pipe, a swirl valve or a tumble valve. When these variable adjusting devices are used in the air path it is possible to calculate the cylinder filling of the internal combustion engine, for example by applying a physical model. The application of such a model is described in EP-A-0 820 559 B1. To be able to apply such a model, however, it is necessary to have a knowledge of the current position of the adjusting device in the air path.
To describe the current position of the adjusting device by applying a model as stated above the adjusting device could be assumed to be functioning correctly and its position could be identified from the control signal of the adjusting device. In an alternative approach the adjusting device is equipped with a sensor providing a position feedback message which delivers the current position to the above-mentioned model or an engine control system. The first alternative, however, has the disadvantage that if the adjusting device is faulty an incorrect position message is delivered to the above-mentioned model or the engine control system. The position feedback approach of the second alternative represents a high-cost technical solution.